1. Field of the Invention
The present invention relates to a battery charger and more particularly, to a battery charger that is adapted to charge different size battery cells, such as AA and AAA battery cells, in which the battery charger can automatically distinguish between different size battery cells in order to provide the battery cell with the proper charging characteristic.
2. Description of the Prior Art
Various portable devices and appliances are known to use multiple rechargeable battery cells, such as AA and AAA battery cells. In order to facilitate charging of the battery cells for such multiple cell appliances, multiple cell battery chargers have been developed. Many known battery chargers are configured to receive battery cells having different sizes, such as AA and AAA battery cells. Because the charging characteristics of different size battery cells are different, various mechanical configurations have been developed to sense the size of the battery cell inserted into the charging terminals of the battery charger and properly configure the battery charger for the correct battery cell.
For example, U.S. Pat. Nos. 5,606,238; 6,384,575; and 6,610,941 disclose battery chargers with different mechanical configurations for detecting the size of a battery cell. For example, Rayovac U.S. Pat. No. 5,606,238 discloses a mechanical configuration for sensing the size of a battery cell inserted into the battery charger for charging. A front wall of the battery compartment is formed with a number of apertures sized to coincide with the diameter of various battery cell cathodes. The apertures are located so that when a battery cell is fully inserted within the battery compartment, the cathodes of the cell are received in one of the apertures. The cathode contacts are disposed behind the apertures. The anode in the battery compartment is formed from a leaf spring and is used to bias the battery cell toward the cathode. There are several problems with such a configuration. For example, the mechanical sensing configuration is dependent upon the diameter of the cathode which varies from manufacturer to manufacturer. In addition, the leaf spring may eventually lose its spring tension due to metal fatigue.
U.S. Pat. No. 6,384,575, assigned to Delta Electronics, Inc. of Taiwan, discloses a different type of battery cell mechanical sensing arrangement for a battery charger. This battery charger includes a anode contact and a rotatable cathode contact. When the rotatable cathode contact is in a first position, it is adapted to receive a battery cell of a first longer length. In a second position, the pivotal cathode contact is adapted to receive battery cells of a shorter length. The mechanical sensing arrangement disclosed in the '575 patent requires the user to rotate the rotatable contact before inserting the battery cell in the battery compartment in order to select the appropriate configuration for the battery cell to be charged. Such an operation is cumbersome for the user.
U.S. Pat. No. 6,610,941 discloses another configuration for mechanically sensing the size of the battery cell. This arrangement uses a slide device and a two-prong fork. The configuration disclosed in the '941 patent is used to sense AAA, AA, C, and D-type batteries. The two-prong fork is pivotally mounted. The prongs of the fork are spaced apart at a distance less than the diameter of a type-C battery. The two-prong fork is also rotatably mounted so that when a type-C or D battery is inserted into the battery compartment, a two-prong fork is pushed downwardly. The actuation of the two-prong fork operates a switch which provides an electrical representation of whether type C/D or type AA/AAA batteries have been installed in the battery compartment. The anode is connected to a slider assembly, which, in turn, actuates a switch depending on the length of the battery cell inserted into the battery compartment. Thus, the combination of the two switches can be used to identify the type of battery that has been inserted into the battery compartment.
Such mechanical systems for sensing the size of a battery cell are relatively cumbersome and are subject to wear and are relatively expensive. As such, systems have been developed for electronically determining the size of a battery cell. For example, commonly owned U.S. Pat. Nos. 5,764,030 and 5,998,966 disclose a system for electrically-sensing the battery size and type of smart batteries. Such smart batteries normally include an internal microprocessor that is adapted to communicate with a microprocessor in the battery charger and thus provide data to the battery charger relating to the size of battery cells in the smart battery pack. Unfortunately, the techniques disclosed in the '030 and '966 patents are not suitable for batteries other than smart battery packs.
Fujitsu, U.S. Pat. No. 5,861,729, discloses a battery charger which can electrically distinguish between NiH and NiCd battery based on [FILL IN DETAILS]. Thus there is a need for a battery charger which can effectively and inexpensively distinguish between different size battery cells which are not part of a smart battery pack.